Crystal structures of rac-2,3-diphenyl-2,3,5,6-tetrahydro-4H-1,3-thiazine-1,1,4-trione and N-[(2S,5R)-1,1,4-trioxo-2,3-diphenyl-1,3-thiazinan-5-yl]acetamide

The syntheses and crystal structures of two thiazinone compounds, in an enantiopure form, are reported. The thiazine rings in the two structures differ in their puckering, as a half-chair in the first and a boat pucker in the second.


Structural commentary
Compound 1 has one chiral center at C1 with an S configuration in the arbitrarily chosen asymmetric unit but crystal symmetry generates a racemic mixture (space group P2 1 /c). Compound 2 has two chiral centers, at C1 and C3 (S and R respectively), synthesized as such, and crystallizes in space group P2 1 2 1 2 1 . In 1, the dihedral angles between the thiazine ring (all atoms) and the pendant C5-C10 and C11-C16 phenyl groups are 84.02 (14) and 79.56 (12) , respectively; the dihedral angle between the pendant rings is 61.26 (15) . The equivalent angles in 2 are 81.25 (15), 82.58 (13) and 50.40 (15) , respectively.

Supramolecular features
In both structures, only C-HÁ Á ÁO-type hydrogen-bond interactions between symmetry-related molecules are observed (Tables 1 and 2 The asymmetric unit of 2 with displacement ellipsoids drawn at 50% probability level.

Figure 3
Overlay plot of 1 and 2 where the three atoms S1, N1, and C11 are matched. Atoms C3 and C8 of compound 1 are labeled.

Figure 1
The asymmetric unit of 1 with displacement ellipsoids drawn at 50% probability level. form a pair of parallel interactions (Fig. 4). In 2 (Fig. 5), the carbon atoms C1 and C4, both of the thiazine ring, as well as C8 of one of the phenyl rings each donate an H atom for three distinct interactions involving three of the four oxygen atoms in the molecule. Although both compounds each have two phenyl rings, neither of the lattices exhibit anystacking interactions.

Synthesis and crystallization
General oxidation procedure (Surrey et al., 1958;Silverberg, 2020;Cannon et al. 2015): the heterocycle (0.267 mmol) was dissolved in glacial acetic acid (1.2 ml). An aqueous solution of KMnO 4 (0.535 mmol in 1.45 ml water) was added dropwise at room temperature with vigorous stirring. The reaction was followed by TLC. Solid sodium bisulfite (NaHSO 3 /Na 2 S 2 O 5 ) was added until the mixture remained colorless and then 1.45 ml of water were added and stirred for 10 min. The mixture was extracted with CH 2 Cl 2 (3 Â 5 ml). The organics were combined and washed once with sat. NaCl. The solution was dried over Na 2 SO 4 and filtered. The product was purified by chromatography in a silica gel micro-column.

Funding information
Research reported here was conducted on instrumentation funded by NSF (for Bruker AXS system) CHEM-0131112, and SIG S10 grants of the National Institutes of Health (for the Rigaku rotating anode system) under award numbers 1S10OD028589-01 and 1S10RR023439-01 to Dr Neela Yennawar.

Special details
Experimental. The data collection nominally covered a full sphere of reciprocal space by a combination of 4 sets of ω scans each set at different φ and/or 2θ angles and each scan (10 s exposure) covering -0.300° degrees in ω. The crystal to detector distance was 5.82 cm. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.